1. Field of the Invention
The invention relates to a belt drive apparatus and an image forming apparatus.
2. Description of Related Art
In conventional image forming apparatus, such as printers, photocopiers, fax machines, and multifunction printers, or in an electrophotographic printer, for example, the surface of a photosensitive drum is uniformly charged by a charge roller and is exposed by an LED head to form an electrostatic latent image, the electrostatic latent image is developed by a developing unit to form a toner image on the photosensitive drum, the toner image is transferred onto a paper sheet, and the transferred toner image is fixed on the paper sheet.
A conventional electrophotographic printer is equipped with a belt drive apparatus to convey paper sheets to a transferring position located between the photosensitive drum and the transferring unit. The belt drive apparatus includes a drive roller, an idle roller, and an endless belt serving as a belt member stretched by the drive roller and the idle roller. When the drive roller rotates, the endless belt is made to run as the idle roller is driven accordingly, thereby conveying the paper sheet on the endless belt to the transferring position.
While the endless belt of the belt drive apparatus is running, the endless belt sometimes moves in the crosstrack direction of the belt and may snake back and forth in that direction. If this occurs, conveyance of the paper sheet becomes unstable, which causes unsatisfactory transfer of the developer image onto the paper sheet. As a consequence, the transferred image quality is degraded.
To address this problem, the snaking of the endless belt is prevented by providing a pulley at least at one end of either the drive roller or the idle roller (the idle roller, for example).
FIG. 2 is a sectional view illustrating an idle roller of the related art, and FIG. 3 is a perspective view illustrating the idle roller of the related art.
These drawings show idle roller 200, pulley 203 provided at one end of idle roller 200, belt receiving portion 204 of pulley 203, and endless belt 210.
If endless belt 210 moves in its width direction and an edge portion of endless belt 210 is brought into contact with belt receiving portion 204 of pulley 203, endless belt 210 is prevented from moving further in that direction. Accordingly, the snaking of endless belt 210 can be prevented (see, for example, JP 2006-162659A).